ARGYLE — Hundreds of volunteers joined a search for a 3-year-old girl here Tuesday night, but she was finally located in the last place anyone wanted to find her — the bottom of a septic tank.

Alisandra Galvan, daughter of Vance and Myla Galvan, was declared dead at the scene about 12:30 a.m. Wednesday. The Galvans are members of an extended family that has owned several upscale Mexican restaurants in the Dallas area

Argyle police Capt. Temple Cottle said investigators had found nothing to indicate that the death was anything but a tragic accident. The child’s body was taken to the Tarrant County medical examiner’s office for an autopsy.

The little girl didn’t come in with the other children who were playing in the backyard of the Galvan home in the 400 block of East Hickory Ridge Circle. Her mother called 911 about 6:45 p.m., saying the girl had been missing for about 15 minutes.

Argyle police soon were joined by search teams from all over Denton County in an effort to find the girl.

“She was outside playing ball with her brother and young uncles, and they came inside and she didn’t,” Cottle said. “They started looking for her, and when they didn’t find her immediately, they called us.”

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Alisandra Galvan’s body was found at the bottom of a septic tank early Wednesday in Argyle.

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Cottle quickly called for help from the Argyle Fire Department, and several other search teams from other agencies and hundreds of volunteers joined the search.

“We finally had so much help that I had to start turning them down,” he said.

Several homes in the neighborhood have small ponds, and divers searched those areas, Cottle said.

The house sits on five acres in a new neighborhood on Hickory Ridge Circle off Hickory Hill Road. The house is serviced by septic tanks. Cottle said the family has lived there less than a month. He said the septic system had three lids — two in the backyard and one outside the yard.

“When we got there, one of the lids in the yard was off. We focused on that as an immediate point of interest, but we also did an immediate ground search and searched the house several times.”

Officers probed the tank but could not find anything that way. When it was apparent that the child was not nearby, police asked for a septic company to respond. A pump truck emptied the tank.

Cottle said investigators have not determined how the child fell into the tank or whether the lid had been removed at an earlier time.

“When it was empty, we found her at the bottom,” Cottle said. “We don’t know at this point how the lid came off or when it came off. The family was shocked to learn it was off. We’re still investigating that.”

Lisa Galvan, Alisandra’s grandmother who lives at the home with her family, said the family had just moved from Plano to live in the country. She said her husband noticed that the drain cover was open Tuesday night and did not think it had been like that a few days ago. She said the top was flimsy and did not have screws to hold it in place.

Grandmother Sandra Byrne said she had stepped on the cover a few days ago and did not think anything of it.

Family members remembered the little girl who loved to sing and play the piano. She was named after her two grandmothers.

“She was my little princess,” Lisa Galvan said. “She was amazingly funny for her age and full of spirit. We always thought she would grow up to be an entertainer.”

Family members were devastated, the police captain said, and it was a sad time for the law enforcement officers who had hoped to find her alive.

“Every time you work one of these, you hope it’s the last time,” Cottle said. “But it never is.”

The Dallas Morning News’ Dan X. McGraw contributed to this report.

DONNA FIELDER can be reached at 940-566-6885. Her e-mail address is dfielder@dentonrc.com .